Oil burners for heating systems conventionally comprise a combustion chamber into which fuel is continually fed via a nozzle.
Oil burners, particularly larger burners, are subject to resonance vibrations, the vibration behaviour of which in oil burners is caused by the combustion space and the nature of the air feed which together form a resonant body.
In the case of gas burners, operated at the resonant frequency, as is described for instance in WO 92/08928 or WO 82/00097, the causes of such vibrations are known and the thereby resulting disadvantages are combated by a variety of means.
Due to the inertia of the gas flowing into a feed pipe a vacuum materializes in the combustion chamber following combustion, as a result of which, on the one hand, gas and air are drawn in and, on the other, a return flow of hot combustion gases occurs which ignite the subsequent fuel mixture inflow. Accordingly, a cyclic process materializes which pulsates at a frequency which substantially depends on the dimensioning of the combustion chamber and feed pipe or feed conduit and the nature of the gas concerned.
Such pulsed operated burners may also create an enormous noise which is in the range of roughly 90 to 140 db(A). This is why in WO 92/08928 a system is provided which decouples the resonance system of the combustion chamber and fuel feed conduit acoustically from the downstream heat exchanger. The resonant frequency occuring in the case of these pulsed burners is of the order of a few 100 Hz and depends on the shape and size of the cavities formed by the combustion chamber and feed conduits.
In the case of gas burners an attempt is also made to prevent the occurence of resonance vibrations by means of damping cavities which are arranged around the gas feed conduit. One such arrangement is known, for example, from DE 33 24 805 A1.
As far as simple small oil burners are concerned which are suitable for operating the heating systems of small houses and should not in general be operated pulsed, resonance vibrations occuring may not only create a noise nuisance, but also result in the oil burner being ruined.
In addition to this, it is known that oil burners as compared to gas burners pose a greater emission problem, caused, on the one hand, by the constitutents contained in the fuel oil and, on the other, by a poorer atomization of occasionaly viscous oil in the combustion chamber so that it is difficult to achieve completely stoichiometric combustion. Also, the oil feed conduits for the continual oil feed tend to dribble which results in a poor combustion as regards emission pollution.
For internal combustion engines very many different kinds of fuel injection devices have been known for a long time. These fuel injection devices are, as a rule, configured as a pumped nozzle system. The pumps employed are solenoid-operated, in which the plunger of the pump is impacted by a solenoid-actuated armature. A variety of pumps having piezoelectric actuators is also known.
In DE-OS 23 07 435 a fuel injection device for internal combustion engines is described in which the pump working space is connected to the pressure space of at least one hydraulically actuatable spring-loaded injection valve by an electrically driven plunger pump and is in connection with a source of pressure via a feed valve. On commencement of the pumping action the plunger exercises a certain idle stroke as a result of which the mass of the plunger is accelerated prior to the actual pumping stroke and the stored kinetic energy is made use of to boost the pressure in the pump working space. For this purpose the injection device comprises as the plunger a soft iron armature which is driven by a linear motor over a relatively long distance.
Such injection devices operating on the energy-storage principle have subsequently been further developed, corresponding injection devices being known from DD-PS 120 514 and DD-PS 213 427. These fuel injection devices operating on the solid-state energy storage principle accelerate the armature of the solenoid and thus the fuel fluid column over a lengthy distance before the pressure is built up needed to eject the the fuel via the nozzle. These fuel injection devices have the advantage that they suffice with little driving energy and achieve a high working frequency due to the small masses which need to be moved. In addition to this they achieve high pressures.
In accordance with DD-PS 120 514 the fuel delivery unit through which the delivery plunger passes is provided in a first section with an axial arrangement of grooves through which the fuel is able to flow off without building up any substantial pressure thereby, this materializing in the subsequent second section of the fuel delivery unit having no fluid outflow grooves. The delivery plunger is accordingly decelerated by the incompressible fuel, as a result of which a pressure is built up in the fuel which overcomes the resistance of the injection valve so that injection of the fuel materializes. The drawback in this arrangement is that when the delivery plunger plunges into the closed section of the barrel unfavorable gap conditions, namely a large gap width and a small gap length, result in high pressure losses which unfavorably affect the build-up in pressure needed for ejection. This is why it is proposed in DE-PS 213 472 to arrange for an impacter on the barrel so that the loss in pressure despite relative large gap widths is maintained reasonably small. However, here the drawback is that impacter action produces wear of the bodies impacting each other. Furthermore, due to impact the impacter is excited to cause longitudinal vibrations which translate to the fuel where they, as high-frequency pressure fluctuations, have an unfavorable effect on the injection procedure.
From WO 93/18297 a further fuel injection device is evident which operates on the principle of solid-state energy storage. In this arrangement partial quantities of the fuel to be ejected are displaced prior to ejection in the pumping region by a plunger element guided in a pump barrel of a plunger pump actuated by a solenoid during the practically zero-resistance acceleration phase in which the plunger element stores kinetic energy and the displacement is suddenly halted by the means interrupting displacement so that a pressure surge is generated in the fuel located in an enclosed pressure space by the the stored kinetic energy of the plunger element being translated directly to the fuel located in the pressure space. This pressure surge is employed to eject the fuel by an injection nozzle device, the means generating the pressure surge, interrupting displacement are arranged outside of the guiding, fluid-tight contact zone between plunger element and plunger barrel of the plunger pump as a result of which the injected fuel amount can be controlled with high frequency and excellent accuracy. In particular, even small quantities of fuel can be injected precisely metered. A further fuel injection device for internal combustion engines operating on the principle of energy storage is known from WO 92/14925. The configuration of one such conventional injection device will now be described in more detail with reference to FIG. 23. From a fuel tank 601 fuel is fed by means of a fuel pump 602 at a pressure of approximately 3 to 10 bar into a pipe 605 in which a pressure regulator 603 and a damping means 604 are arranged. At the end of the conduit 605 a, for example, solenoid-actuated shut-off valve 606 is provided via which, in the open condition, fuel is fed back accelerated by the pump 602 into the storage tank 601. By abruptly closing the shut-off valve 606 the kinetic energy of the fuel flowing in the conduit 605 and in the conduit 607 is converted into pressure energy. The magnitude of the thereby resulting pressure surge is in the region of 20 to 80 bar, i.e. roughly ten times the flow pressure generated by the pump 602 in the conduit 605 which is also termed a swing pipe. The thus resulting pressure surge at the shut-off valve 606 is made use of to eject the fuel accelerated in this way via an injection nozzle 610 which is connected via a pressure conduit 609 to the valve 606 and thus to the conduit 605.
Due to employing an solenoid-actuatable shut-off valve this known injection device is electronically controllable, more particularly by means of an electronic control unit 608 connected to the valve 606.
The drawback in this fundamental configuration of the injection device which works by energy stored in the fuel, is that priming is necessary to furnish the energy needed to accelerate the fuel fluid column in the swing pipe and which operates continually. This continually operating priming necessitates means for maintaining the flow constant. For this purpose the fuel flow delivered in excess by the pump 602 is diminished by the pressure regulating valve 603 which is in connection with the storage tank 601 via a return conduit. Diminishing the pressure results in a loss of energy and accordingly, in addition to an increase in fuel temperature, in changes in pressure at the injection valve 606, as a result of which the accuracy of injection is impaired. In addition to this, the pressure regulating valve 602 always necessitates a minimum reduced control amount to be able to operate stably which makes for a further loss in energy. Since the flow volume requirement at the injection nozzle 10 depends on the engine speed as well as on the amount to be ejected every time the pressure supply means needs to deliver the flow for full load operation already on idle so that relatively high quantities of fuel need to be reduced by control via the pressure regulating valve 603 with a corresponding loss in energy for the system as a whole.
This is why it is proposed in WO 92/14925 to make the fuel flow required for injection available for each injection procedure only as long as this is necessary as a function of the engine operating conditions in keeping with time and flow requirements. By employing an intermittently operated fuel acceleration pump the need for continual priming is eliminated which is in favor of the energy balance of the injection device. Furthermore, utilization of available energy is optimized by employing a common control means for the acceleration pump and the electrically actuatable delay means, for example by way of a solenoid-actuatable shut-off valve.
Preference is given to a solenoid-actuated plunger pump as the fuel acceleration pump for intermittent operation. However, a diaphragm pump for fuel acceleration may also be provided within the pressure surge means. Instead of an electromagnetic pump drive an electrodynamic, a mechanical or a drive means piezoelement may be provided.
By signalling pump and delay means in common not only the timing of the pump and of the delay means can be optimally adapted but also the frequency and volume of injection can be freely selected by employing a common control, this applying in particular when use is made of a fuel injection device operating on the principle of solid-state energy storage.
It can thus be summarized that prior art provides for, on the one hand, oil burners operating continually which have certain drawbacks, particularly by failing to always satisfy the desired requirements due to resonances and their emission pollution in the case of pressure oscillations and, on the other, a very great variety of injection devices, long since known, in the case of internal combustion engines which are designed especially for the control of small amounts of fuel.